This invention relates to a modular conveyer chain, and more particularly to an improved chain link for use in construction of a modular conveyer chain.
Manufacturing and production facilities utilize modular conveyer chains to transport products or articles of production from one location to another. Conventional modular conveyor chains are typically comprised of multiple thermoplastic chain links or modules. The links making up the modular conveyer chain typically have a plurality of spaced link ends which intermesh with complementary spaced link ends projecting from a link or links in an adjacent row. The individual chain links are usually similar in width and may be arranged in a bricked configuration. The intermeshing link ends are joined or hinged together by a connecting pin that permits the adjacent chain links to pivot with respect to each other.
The chain links are typically joined together to form an endless conveyor chain that is usually driven by a drive sprocket. The modular conveyor chains are subjected to tensile forces that tend to separate the individual chain links when the chain is placed under a load.
Conventional chain links are typically made of thermoplastic (e.g. acetal, polyester, nylon and polypropylene). The choice of the polymer used for the chain link usually depends on the physical properties which are desired (i.e. high tensile strength, high fatigue strength, low friction, chemical resistance and/or suitability for use under extreme cyclic temperatures) in the chain link. The tensile strength and fatigue strength of the chain link are especially important because a chain link having these increased mechanical properties increases the overall tensile strength of the modular conveyor chain and reduces chain stretch due to loading.
Modular conveyer chains are often used to carry goods from one location to another location where the temperature of the environment at the two locations is significantly different. The individual chain links expand as the temperature of the chain increases, and contract as the temperature of the chain decreases. As the individual chain links expand or contract, the overall length of the conveyer chain varies significantly as a result of a high coefficient of thermal expansion that is commonly associated with most thermoplastics.
A typical application where a modular conveyor belt is subject to extreme cyclic temperatures is in a conveyor chain used to transport cans or bottles through pasteurizers in breweries. The high temperatures in a pasteurizer combined with the slow movement of the cans or bottles through the pasteurizer when the chain is under a tensile load may cause the chain to stretch such that the bottom canteary section of an endless conveyer chain sags. This chain stretching may also effect the performance of the interaction between the drive sprocket and chain links. In addition, in double deck conveyor systems, the sagging can become so great that the bottom canteary section of the top conveyor of an endless conveyer chain interferes with bottles located on a lower conveyor chain.
One known method for increasing the tensile strength and the fatigue strength of the overall modular conveyor chain is to use metal links in combination with the thermoplastic chain links. The combination of thermoplastic links and metal links causes the loads on the modular conveyer to be carried primarily by the metal links. One of the problems associated with combining links made from two different materials to form a modular conveyor is that there are significant bending stresses generated within the thermoplastic chain links due to the differences in the modulus of elasticity, coefficient of friction and coefficient of thermal expansion between the thermoplastic chain links and the metal chain links.
Plastics manufacturers have increased the tensile strength of thermoplastics by adding filler to the polymer as the raw polymer is being manufactured. The filler is typically in the form of long fibers. Manufacturers of long fiber reinforced thermoplastics, such as Ticona and DuPont, provide technical literature to their customers which indicates that increasing the amount of filler within the raw polymer increases the tensile strength of the molded polymer. The technical literature also provides results for tensile tests performed on different thermoplastics where the percentage of filler within the polymer varies. The tests were performed in accordance with ASTM standards and indicate that the tensile strength of the thermoplastics increases as the weight percent of filler within the raw polymer increases. The technical literature shows test results for polymers that include up to 60 weight percent filler within the polymer.